Mammoth Uncensored Word List:
53 words ending with gs, 15 letters long

attitudinisings attitudinizings backscatterings backscratchings bioengineerings bioprospectings bremsstrahlungs countershadings cybersquattings electioneerings electrofishings electroformings electrogildings electroplatings electrowinnings featherbeddings fingerprintings foreshortenings fortunetellings gerrymanderings goodfornothings groundbreakings huckleberryings immunoblottings leatherworkings malfunctionings microcomputings micromarketings mountaineerings multithreadings neurocomputings neuromarketings nonengineerings nonoverlappings pamphleteerings photoengravings photofinishings quicksilverings reconditionings rumormongerings scaremongerings schoolteachings showerproofings silversmithings steeplechasings strikebreakings subcontractings supercomputings teleprocessings thimbleriggings wappenschawings weltanschauungs whistleblowings